In the hydrocarbon recovery industry, pumps are used at the lower ends of wells to pump oil to the surface through production tubing positioned within a well casing. Power is transmitted to the pump from the surface using a rod string positioned within the production tubing. Rod strings include both “reciprocating” types, which are axially stroked, and “rotating” types, which rotate to power progressing cavity type pumps. The latter type is increasingly used, particularly in wells producing heavy, sand-laden oil or producing fluids with high water/oil ratios.
Both reciprocating and rotating rods benefit from the use of rod guides to protect the interior surface of the production tubing. In practice, sucker rods and production tubing do not hang perfectly concentrically within a well, in part because well bores are never perfectly straight. Direct contact between the rod and the production tubing during reciprocation or rotation, especially while immersed in a harsh fluid environment, would otherwise cause expensive damage to the tubing and the rod. Rod guides are therefore placed between the rod and the tubing as a low cost sacrificial wear member.
Some rod guides have a plurality of fins projecting radially toward the ID of the production tubing, to center the rod within the tubing. The space between fins then provides a flow path for drilling fluid or hydrocarbon production flowing through the tubing. U.S. Pat. No 6,152,223 to Abdo describes such a rod guide, incorporating a low-friction wear material and a fin construction affording generous flow through. Other rod guides have a generally cylindrical outer surface having an OD substantially less than the ID of the production tubing, such that there is ample space between the guide and the tubing as a flow path. The disadvantage of this type of guide is there is less erodible wear volume (“EWV”) in the guide, which leads to greater frequency of replacement and associated costs.
Many rod guides require at least some assembly to the rod prior to being transported to the field where they will be used. U.S. Pat. No. 5,941,312 to Vermeeren and U.S. Pat. No. 5,339,896 to Hart, et. al, each disclose examples of such “partially field-installable” rod guides. A spool is mechanically bonded to the rod in a shop or manufacturing facility. When in the field, an outer rod guide body may be later snapped over the spool affixed to the rod.
The Hart patent describes a rod guide having embodiments for use with both rotating and reciprocating rods. The embodiment of the outer guide body depends on whether it is to be used with a reciprocating or rotating rod. For example, for a rotating embodiment, the body and spool may rotate freely with respect to each other, which is generally preferred for all rotating type rod guides. As the rod rotates, the spool remains stationary with respect to the rod, while the outer body is free to rotate about the spool to remain nearly stationary with respect to a sidewall of the production tubing, minimizing wear between the body and the tubing, and between the spool and the rod. The majority of the wear instead occurs between the low cost sacrificial spool and guide body. For a reciprocating embodiment, the spool may include an elongate projection, and the outer guide body may include a slot for mating with the projection, such that the guide body does not rotate with respect to the spool.
To minimize manufacturing and assembly costs, some existing rod guides can be installed entirely in the field. U.S. Pat. No. 4,858,688 to Edwards, et al. and U.S. Pat. No. 5,494,104 to Sable each disclose examples of such “fully field-installable” rod guides. In each of these, a generally unitary body is provided with a bore for tightly positioning about a rod, and an access channel is provided from an outer surface of the body to the bore, allowing the guide to be forcibly “snapped-on” in the field. A problem inherent to each of these rod guides is that the single-piece body must be flexed when snapped onto the rod, weakening the gripping power of the guide. The Sable patent strives to minimize this drawback, by providing a non-circular bore to place more material at the area of highest flex. Although this potentially improves the gripping power of the guide, the presence of the access channel remains a source of structural weakness during the service life of the guide. A further shortcoming of these single-piece snap-on rod guides is that a single-piece body is generally best suited for reciprocating-type rods, and is non-ideal for use with rotating type rods.
U.S. Pat. No. 4,343,518 discloses another type of fully field-installable rod guide that does not require an access channel for installation. Instead, the rod guide comprises two half sections which are adapted to be lockingly clamped together. One half section has grooves and the other half section includes flanges having complementary tapered surfaces so that when the two half sections are moved together vertically the flanges are wedged in the grooves to clamp the two half sections together about the rod. The tapered surfaces are very narrow, however, and do not alone produce sufficient gripping power. The half sections may use inner ridges on semi-circular recesses for contacting the rod, to cause the recesses to deform into an elliptical shape to resist slippage. Another shortcoming of the rod guide is that it is described for use only with a reciprocating type rod, and is unsuitable for use with a rotating type rod.
A rod guide is desired that is fully field-installable, useful with both reciprocating and rotating rods, and having an improved mechanism for attaching the guide to the rod.